Electrode materials with high surface conductivity

ABSTRACT

The present invention concerns electrode materials capable of redox reactions by electrons and alkaline ions exchange with an electrolyte. The applications are in the field of primary (batteries) or secondary electrochemical generators, super capacitors and light modulating system of the super capacitor type.

FIELD OF INVENTION

[0001] The present invention concerns electrode materials capable ofredox reactions by electrons and alkaline ions exchange with anelectrolyte. The applications are in the field of primary (batteries) orsecondary electrochemical generators, superapacitors and lightmodulating system of the electrochromic type.

BACKGROUND OF THE INVENTION

[0002] Insertion compounds (hereinafter also referred to aselectroactive materials or redox materials) are well known, and theiroperation is based on the exchange of alkaline ions, in particularlithium ions, and valence electrons of at least one transition element,in order to keep the neutrality of the solid matrix. The partial orcomplete maintenance of the structural integrity of the material allowsthe reversibility of the reaction. Redox reactions resulting in theformation of several phases are usually not reversible, or onlypartially. It is also possible to perform the reactions in the solidphase through the reversible scission of the sulphur-sulphur bonds orthe redox reactions involved in the transformation of the aromaticorganic structures in quinonoid form, including in conjugated polymers.

[0003] The insertion materials are the electrochemical reactions activecomponents used in particular in electrochemical generators,supercapacitors or light transmission modulating system (electrochromicdevices).

[0004] The progression of the ions-electrons exchange reaction requiresthe existence within the insertion material of a double conductivity,simultaneous with the electrons and the ions, in particular lithiumions, either one of these conductivities being eventually too weak toensure the necessary kinetic exchanges for the use of the material, inparticular for electrochemical generators or superapacitors. Thisproblem is partly solved by using so-called “composite” electrodes,wherein the electrode material is dispersed in a matrix containing theelectrolyte and a polymer binder. When the electrolyte is a polymerelectrolyte or a polymer gel working in the presence of a solvent, themechanical binding role is carried out directly by the macromolecule.Gel means a polymer matrix, solvating or not, and retaining a polarliquid and a salt, to confer to the mixture the mechanical properties ofa solid while retaining at least a part of the conductivity of the polarliquid. A liquid electrolyte and the electrode material can also bemaintained in contact with a small fraction of an inert polymer binder,i.e., not interacting with the solvent. With any of these means, eachelectrode material particle is thus surrounded by an electrolyte capableof bringing the ions in direct contact with almost the totality of theelectrode material surface. To facilitate electronic exchanges, it isusual, according to the prior art, to add particles of a conductivematerial to one of the mixtures of the electrode material andelectrolyte mentioned above. Such particles are in a very divided state.Generally, carbon-based materials are selected, and especially carbonblacks (Shawinigan or Ketjenblack®). However, the volume Fractions usedmust be kept low because such material modifies strongly the rheologytheir suspension, especially in polymers, thereby leading to anexcessive porosity and loss of operating efficiency of the compositeelectrode, in terms of the fraction of the usable capacity as well asthe kinetics, i.e, the power available. At these low concentrationsused, the carbon particles structure themselves in chains, and thecontact points with the electrode materials are extremely reduced.Consequently, such configuration results in a poor distribution of theelectrical potential within the electroactive material. In particular,over-concentrations or depletion can appear at the triple junctionpoints;

[0005] These excessive variations of the mobile ions localconcentrations and the gradients within the electroactive materials areextremely prejudicial to the reversibility of the electrode operationover a high number of cycles. These chemical and mechanical constraintsor stresses, result at the microscopic level in the disintegration(particulation) of the electroactive material particles, a part of whichbeing susceptible to lose the contact with the carbon particles and thusbecoming electrochemically inactive. The material structure can also bedestroyed, with the appearance of new phases and eventual release oftransition metal derivatives, or other fragments in the electrolyte.These harmful phenomenons appear even more easily the larger the currentdensity or the power requested at the electrode is.

IN THE DRAWINGS

[0006]FIG. 1 illustrates the difference between a classic electrodeaccording to the prior art (A) and an electrode according to theinvention wherein the electroactive material particles are coated with acarbonaceous coating (B).

[0007]FIGS. 2 and 3 illustrate a comparison between a sample of LiFePO₄coated with a carbonaceous deposit, with an uncoated sample. The resultswere obtained by cyclic voltammetry of LiFcPO₄/POE₂₀LiTFSI/Li batteriescycled at 20 mV.h⁻¹ between 3 and 3.7 volts at 80° C. The first cycle isshown on FIG. 2, and the fifth on FIG. 3.

[0008]FIG. 4 illustrates the evolution of capacity during cycling forbatteries containing carbonaceous and non-carbonaceous LiFePO₄ samples.

[0009]FIG. 5 illustrates the performances of a battery containingcarbonaceous LiFcPO₄ and cycled under an intentiostatic mode between 3and 3.8 V at 80° C. with a charge and discharge speed corresponding toC/l.

[0010]FIG. 6 illustrates the evolution of the current vs. time of aLiFePO₄/gamma-butyrolactone LiTFSI/Li containing a carbonaceous sampleand cycled at 20 mV.h⁻¹ between 3 and 3.7 V at room temperature.

[0011]FIG. 7 illustrates the evolution of the current vs. time of aLiFePO₄/POE₂₀LiTFSI/Li containing a carbonaceous sample.

[0012]FIGS. 8 and 9 illustrate a comparison between carbonaceous andnon-carbonaceous LiFePO₄ samples. cycled. The results have been obtainedby cyclic voltammetry of LiFePO₄/POE₂₀LiTFSI/Li batteries cycled at 20mV.h⁻¹ between 3 and 3.7 volts at 80° C. The first cycle is shown onFIG. 8, and the fifth on FIG. 9.

[0013]FIG. 10 illustrates the evolution of the capacity during cyclingof batteries prepared with carbonaceous and non-carbonaceous LiFePO₄samples.

SUMMARY OF WE INVENTION

[0014] In accordance with the present invention, there is provided anelectrode material comprising a complex oxide corresponding to thegeneral formula A_(a)M_(m)Z_(z)O_(o)N_(n)F_(f) wherein:

[0015] comprises an alkaline metal;

[0016] M comprises at least one transition metal, and optionally atleast one non-transition metal such as magnesium or aluminum; andmixtures thereof;

[0017] Z comprises at least one non-metal;

[0018] O is oxygen; N nitrogen and F is fluorine; and the coefficientsa, m, z, o, n, f≧0 and are selected to ensure electroncutrality, whereina conductive carbonaceous material is deposited homogeneously on asurface of the material to obtain a substantially regular electric fielddistribution on the surface of material particles. The similarity inionic radii between oxygen, fluorine and nitrogen allows mutualreplacement of these elements as long as electroneutrality ismaintained. For simplicity and considering that oxygen is the mostfrequently used element, these materials are thereafter referred to ascomplex oxides. Preferred transition metals comprise iron, manganese,vanadium, titanium, molybdenum, niobium, tungsten, zinc and mixturesthereof. Preferred non-transition metals comprises magnesium andaluminum, and preferred non-metals comprise sulfur, selenium,phosphorous, arsenic, silicon, germanium, boron, and mixtures thereof.

[0019] In a preferred embodiment, the final mass concentration of thecarbonaceous material varies between 0.1 and 55%, and more preferablybetween 0.2 and 15%.

[0020] In a further preferred embodiment, the complex oxide comprisessulfates, phosphates, silicates, oxysulfates, oxyphosphates,oxysilicates and mixtures thereof, of a transition metal and lithium,and mixtures thereof. It may also be of interest, for structuralstability purposes, to replace partially the transition metal with anelement having the same ionic radius but not involved in the redoxprocess. For example, magnesium and aluminum, in concentrationspreferably varying between 1 and 25%.

[0021] The present invention also concerns electrochemical cells whereinat least one 5 electrode is made of an electrode material according tothe present invention. The cell can operate as a primary or secondarybattery, a supercapacitor, or a light modulating system, the primary ora secondary battery being the preferred mode of operation.

DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention allows the fabrication of electrodematerials of extremely varied compositions with its surface, or most ofit, coated with a uniform coating of a conductive carbonaceous materialdeposited chemically. The presence in the electrode materials of theinvention of a uniform coating, when compared to a punctual contactobtained with carbon powders or other prior art conductive additives,allows a regular distribution of the electrical field at the surface ofthe electroactive material particles. Further, the ions concentrationgradients arc considerably diminished. Such improved distribution of theelectrochemical reaction at the surface of the particles allows on oneside the maintenance of the structural integrity of the material, and onthe other side improves the kinetics in terms of the current density andpower availability at the electrode, because of the greater surfaceaccessible.

[0023] In the present application, carbonaceous material means a solidpolymer comprising mainly carbon, i.e. from 60 to 100% molar, and havingan electronic conductivity higher than 10⁻⁶ S/cm at room temperature,preferably higher than 10 ⁻⁴ S/cm. Other elements that can be presentare hydrogen, oxygen, nitrogen, as long as they do not interfere withthe chemical inertia of the carbon during the electrochemical operation.The carbonaceous material can be obtained through thermal decompositionr dehydrogenation, e.g., by partial oxidation, of various organicmaterials. In general, any material leading, through a reaction or asequence of reactions to the solid carbonaceous material with thedesired property without affecting the stability of the complex oxide,is a suitable precursor. Preferred precursors include, but are notlimited to: hydrocarbons and their derivatives, especially thosecomprising polycyclic aromatic moieties, like pitch and tar derivatives,perylene and its derivatives; polyhydric compounds like sugars andcarbon hydrates and their derivatives; and polymers. Preferred examplesof such polymers include polyolefins, polybutadicnes, polyvinylicalcohol, phenol condensation products, including those from a reactionwith an aldehyde, polymers derived from furfurylic alcohol, polymersderivatives of styrene, divinylbenzene, naphtalene, perylene,acrylonitrile, vinyl acetate; cellulose, starch and their esters andethers, and mixtures thereof.

[0024] The improvement of the conductivity at the surface of theparticles obtained with the carbonaceous material coating according tothe present invention allows the satisfactory operations of electrodescontaining electroactive materials having an insufficient electronicconductivity to obtain acceptable performances. Complex oxides withredox couples in useful voltage range and/or using elements inexpensiveor nontoxic but whose conductivity otherwise would be to low forpractical use, now become useful as electrode materials when theconductive coating is present. The choice of the structures or phasemixtures possessing redox properties but having an electronicconductivity that is too low, is thus much wider than that withcompounds of the prior art, of the lithium and transition metal mixedoxides. It is particularly possible to include within the redoxstructures, at least one element selected from non-metals (metalloids)such as sulphur, selenium, phosphorus, arsenic, silicon or germanium,wherein the greater electronegativity allows the modulation of the redoxpotential of the transition elements, but at the expense of theelectronic conductivity. A similar effect is obtained with the partialor complete substitution of the oxygen atoms with fluorine or nitrogen.

[0025] The redox materials are described by the general formulaA_(a)M_(m)Z_(z)O_(o)N_(n)F_(f) wherein:

[0026] A comprises an alkaline metal such as Li, Na, or K;

[0027] M comprises at least one transition metal, and optionally atleast one a non-transition metal such as magnesium or aluminum; ormixtures thereof;

[0028] Z comprises at least one non-metal such as S, Se, P, As, Si, Ge,B;

[0029] O is oxygen;

[0030] N is nitrogen and F is fluorine, wherein the latter elements canreplace oxygen in the complex oxide because of the ionic radii valuesfor F⁻, O²⁻ and N³⁻ are similar, and

[0031] each coefficient a, m, z, o, n and f≧0 independently, to ensureelectroneutrality of the material.

[0032] Preferred complex oxides according to the invention comprisethose of formula Li_(1+x)MP_(1−x)Si_(x)O₄;Li_(1+x−y)MP_(1−x)Si_(x)O_(4−y)F_(y);Li_(3−x+z)M₂(P_(1−x+z)S_(x)Si_(z)O₄)₃;Li_(3+u−x+z)V_(2−x−w)Fe_(u)Ti_(w)(P_(1−x−z)S_(x)Si_(z)O₄)₃, orLi_(4+x)Ti₅O₁₂, Li_(4+x−2y)Mg_(y)Ti₅O₁₂, wherein w≦2; 0≦x, y≦1; z≦1 andM comprises Fe or Mn.

[0033] The carbonaceous coating can be deposited through varioustechniques that are an integral part of the invention. A preferredmethod comprises the pyrolysis of organic matter, preferablycarbon-rich, in the presence of the redox material. Particularlyadvantageous are mesomolecules and polymers susceptible of easilyforming, either mechanically or by impregnation from a solution orthrough in situ polymerization, a uniform layer at the surface of theredox material particles. A subsequent pyrolysis or dehydrogenation stepthereof provides a fine and uniform layer of the carbonaceous materialat the surface of the particles of the redox material. To ensure thatthe pyrolysis or dehydrogenation reaction will not affect the latter, itis preferred to select compositions wherein the oxygen pressureliberated from the material be sufficiently low to prevent oxidation ofthe carbon formed by the pyrolysis. The activity of the oxygen ofcompounds A_(a)M_(m)Z_(z)O_(o)N_(n)F_(f) can be controlled by theconcentration of alkaline metal, which itself determines the oxidationstate of the transition element or elements contained in the materialand being a part of the invention. Of particular interest are thecompositions wherein the coefficient “a”-of the alkaline metalconcentration allows the maintenance of the following oxidation states:Fe²⁺, Mn²⁺, V²⁺, V³⁺, Ti²⁺, Ti³⁺, Mo³⁺, Mo⁴⁺, Nb³⁺, Nb⁴⁺, W₄₊.Generally, oxygen pressures in the order of 10⁻²⁰ bars at 0° C. and de10⁻¹⁰ bars at 900° C. are sufficiently low to allow the deposition ofcarbon by pyrolysis, the kinetic of carbon formation in the presence ofhydrocarbonaceous residues resulting from the pyrolysis being quickerand less activated than oxygen formation from the redox materials. It isalso possible and advantageous to select materials having an oxygenpressure in equilibrium with the materials that is inferior to that ofthe equilibrium

C+O₂

CO₂

[0034] In this instance, the carbonaceous material can bethermodynamically stable vis-à-vis the complex oxide. The correspondingpressures are obtained according to the following equation:${\ln \quad {P\left( O_{2} \right)}} = {{\ln \quad {P\left( {CO}_{2} \right)}} = \frac{94050}{R\left( {{273\text{,}2} + \theta} \right)}}$

[0035] wherein R is the perfect gas constant (1,987 cal.mole⁻¹.K⁻¹); andθ is the temperature in ° C. TABLE 1 provides oxygen pressures atseveral temperatures: P(O₂) P(O₂) θ (° C.) P(CO₂) = 1 atm P(CO₂) = 10⁻⁵atm 200 3.5 × 10⁻⁴⁴ 3.5 × 10⁻⁴⁹ 300 1.4 × 10⁻³⁶ 1.4 × 10⁻⁴¹ 400 2.9 ×10⁻³¹ 2.9 × 10⁻³⁶ 500 2.5 × 10⁻²⁷ 2.5 × 10⁻³² 600 2.9 × 10⁻²⁴ 2.5 ×10⁻²⁹ 700 7.5 × 10⁻²² 7.5 × 10⁻²⁷ 800 7.0 × 10⁻²⁰ 7.0 × 10⁻²⁵ 900 3.0 ×10⁻¹⁸ 3.0 × 10⁻²³

[0036] It is also possible to perform the carbon deposition through thedisproportionation of carbon oxide at temperatures lower than 800° C.according to the equation:

2CO

C+CO₂

[0037] This reaction is exothermic but slow. The complex oxide particlescan be contacted with carbon monoxide pure or diluted in an inert gas,at temperatures varying from 100 to 750° C., preferably between 300 and650° C. Advantageously, the reaction is carried out in a fluidized bed,in order to have a large exchange surface between the gaseous phase andthe solid phase. Elements and cations of transition metals present inthe complex oxide are catalysts of the disproportionation reaction. Itcan be interesting to add small amounts of transition metal salts,preferably iron, nickel, or cobalt, at the surface of the particles,these elements being particularly active as catalysts of thedisproportionation reaction. In addition to carbon monoxidedisproportionation, hydrocarbons in the gaseous forms can be decomposedat moderate to high temper to yield carbon deposits. Of special interestfor the operation are the hydrocarbons with a low energy of formation,like alkenes, alkynes or aromatic rings.

[0038] In a variation, the deposition of the carbonaceous material canbe performed simultaneously with a variation 6foe composition ofalkaline metals A. To do so, an organic acid or polyacid salt is mixedwith the complex oxide. Another possibility comprises the in situpolymerization of a monomer or monomer mixtures. Through pyrolysis, thecompound deposits a carbonaceous material film at the surface and thealkaline metal A is incorporated according to the equation:

A_(a)′M_(m)Z_(z)O_(o)N_(n)F_(f)+A_(a+a)′C_(c)O_(o)R′

A_(a)M_(m)Z_(z)O_(o)N_(n)F_(f)

[0039] R′ being an organic radical, eventually part of a polymericchain.

[0040] Among the compounds susceptible of permitting this reaction, itcan be mentioned in a non limited manner salts of carboxylic acids suchas oxalic, malonic, succinic, citric, polyacrylic, polymethacrylic,benzoic, phtalic, propiolic, acetylene dicarboxylic, naphthalene di- ortetracarboxylic, perylene tetracarboxylic and diphenic acids.

[0041] Obviously, the pyrolysis of an organic material deprived of analkaline element in combination with an alkaline element salt can alsolead to the desired stoichiometry of the complex oxide.

[0042] It is also possible to obtain a carbonaceous material deposit,especially at low or mid-range temperatures, lower than 400° C., byreduction of carbon-halogen bonds according to the equation:

CY—CY+2e ⁻

—C═C—+2Y⁻

[0043] wherein Y represents a halogen or a pseudo-halogen. The ternpseudo-halogen means an organic or inorganic radical susceptible ofexisting in the form of an ion Y— and formed a corresponding protonatedcompound HY. Examples of halogen and pseudo-halogen include F, Cl, Br,I, CN, SCN, CNO, OH, N₃, RCO₂, RSO₃ wherein R is H or an organicradical. The formation by reduction of CY bonds is preferably performedin the presence of reducing elements such as hydrogen, zinc, magnesium,Ti³⁺ ions, Ti²⁺ ions, Sm²⁺ ions, Cr²⁺ ions, V²⁺ ions,tetrakis(dialkylamino ethylene) or phosphines. These reagents caneventually be obtained or regenerated electrochemically. Further, it canalso be advantageous to use catalysts increasing the reduction kinetic.Palladium or nickel derivatives are particularly efficient, particularlyin the form of complexes with is phosphorous or nitrogen compounds like2,2′-bipyridine. Similarly, these compounds can be generated chemicallyin an active form in the presence of reducing agents, such as thosementioned above, or electrochemically. Compounds susceptible ofgenerating carbon by reduction include perhalocarbons, particularly inthe form of polymers, hcxachlorobutadiene and hexachlorcyclopentadiene.

[0044] Another way to free carbon from a low temperature processcomprises the elimination of the hydrogenated compound HY, Y being asdefined above, according to the equation:

—CH—CY—+B

—C═C—+BHY

[0045] Compounds susceptible of generating carbon from reduction includeorganic compounds comprising an even number of hydrogen atoms and Ygroups, such as hydrohalocarbons, in particular in the form of polymers,such as vinylidene polyfluoride, polychloride or polybromide, or carbonhydrates. The dehydro (pseudo) halogenation can be obtained at lowtemperature, including room temperature, by reacting a base with the HYcompound to form a salt. Example of suitable bases include tertiarybasis, amines, amidines, guanidines, imilazoles, inorganic bases such asalkaline hydroxides, organometallic compounds behaving like strongbases, such as A(N(Si(CH₃)₃)₂, LiN[CH(CH₃)₂]₂, and butyl-lithium.

[0046] In the last two methods, it can be advantageous to anneal thematerial after the carbon deposition. Such treatment improves thestructure or the crystallinity of the carbonaceous deposit. Thetreatment can be performed at a temperature varying between 100 and1000° C., preferably between 100 and 700° C., to prevent the potentialreduction of is the complex oxide by the carbonaceous material.

[0047] Generally, it is possible to obtain uniform carbonaceous materialcoatings, ensuring a sufficient electronic conductivity, i.e. at leaston the same order than the ionic conductivity of the oxide particle. Thethick coatings provide a conductivity sufficient so that the binarymixture of complex oxide particles coated with the carbonaceousmaterial, and the electrolyte, liquid or polymeric or the inertmacromolecular binder to be wetted with thc electrolyte, is conductiveby a simple contact between the particles. Generally, such behaviour canbe observed at volumic fractions comprised between 10 and 70%.

[0048] It can also be advantageous to select deposits of carbonaceousmaterials sufficiently thin to prevent obstruction of the passage ofions, while ensuring the distribution of the electrochemical potentialat the surface of the particles. In this instance, the binary mixtureseventually do not possess an electronic conductivity sufficient toensure the electronic exchanges with the electrode substrate (currentcollector). The addition of a third electronic conductive component, inthe form of a fine powder or fibers, provides satisfactory macroscopicconductivity and improves the electronic exchanges with the electrodesubstrate. Carbon blacks or carbon fibers are particularly advantageousfor this purpose and give satisfactory results at volumic concentrationsthat have little or no effect on the rheology during the use of theelectrode because of the existence of electronic conductivity at thesurface of the electrode material particles. Volumic fractions of 0.5 to10% are particularly preferred. Carbon black such as Shawinigan® orKetjenblack® are preferred. Among carbon fibers, those obtained bypyrolysis of polymers such as tar, pitch, polyacrylonitrile as well asthose obtained by cracking of hydrocarbons are preferred.

[0049] Interestingly, because of its light weight and malleability,aluminium is used as the current collector constituent. This metal isnonetheless coated with an insulating oxide layer. This layer, whichprotects the metal from corrosion, can in certain conditions increasethe thickness, leading to an increase resistance of the interface,prejudicial to the good operation of the electrochemical cell. Thisphenomenon can be particularly detrimental and fast when the electronicconductivity is only ensured, as in the prior art, by the carbonparticles having a limited number of contact points. The use, incombination with aluminium, of electrode materials coated with aconductive carbonaceous material layer increases the exchange surfacealuminium-electrode. The aluminum corrosion effects are thereforecancelled or at least significantly minimized. It is possible to useeither aluminium collectors in the form of sheet or eventually in theform of expanded or perforated metal or fibers, which allow a weightgain. Because of the properties of the materials of the invention, evenin the case of expended or perforated metal, electronic exchanges at thecollector level take place without noticeable increase of theresistance.

[0050] Whenever the current collectors are thermally stable, it is alsopossible to perform the pyrolysis or dehydrogenation directly on thecollector, to obtain after carbon 10 deposition, a continuous porousfilm that can be infiltrated with an ionic conductive liquid, or with amonomer or a mixture of monomers generating a polymer electrolyte afterin situ polymerisation. The formation of porous films in which thecarbonaceous coating forms a chain are easily obtained according to theinvention through pyrolysis of a complex oxide-polymer compositedeposited in the form of a film on a metallic substrate.

[0051] In using the electrode material according to the invention intoan electrochemical cell, preferably a primary or secondary battery, theelectrolyte is preferably a polymer, solvating or not, optionallyplasticized or gelled by a polar liquid comprising in solution one ormore metallic salts, preferably at least a lithium salt. In suchinstance, the polymer is preferably formed from units of oxyethylene,oxypropylene, acrylonitrile, vinylidene fluoride, acrylic acid ormethacrylic acid esters, itaconic acid esters with alkyls or oxaalkylgroups. The electrolyte can also be a polar liquid immobilized in amicroporous separator, such as a polyolefin. a polyester, nanoparticlesof silica, alumina or lithium aluminate LiAlO₂. Examples of polarliquids include cyclic or linear carbonates, alkyl formiates,oligoethylene glycols, α-ω alkylethers, N-methylpyrrolidinone,γ-butyrolactone, tetraalakylsulfamides and mixtures thereof.

[0052] The following examples are provided to illustrate preferredembodiment of the invention, and shall not be construed as limiting itsscope.

EXAMPLE 1

[0053] This example illustrates the synthesis of a material of thepresent invention leading directly to an insertion material coated witha carbonaceous deposit.

[0054] The material LiFePO₄ coated with a carbonaceous deposit isprepared from vivianite Fe₃(PO₄ ₎ ₂.8H₂O and lithium orthophosphateLi₃PO₄ in stoichiometric amounts according to the reaction:

Fe₃(PO₄)₂.8H₂O+Li₃PO₄

3LiFePO₄

[0055] Polypropylene powder in an amount corresponding to 3% by weightof vivianite is added. The three components mixed together intimatelyand ground in a zirconia ball mill. The mixture is then heated under aninert atmosphere of argon, firstly at 350° C. for 3 hours to dehydratethe vivianite. Subsequently, the temperature is risen gradually up to700° C. to crystallize the material and carbonize the polypropylene. Thetemperature is maintained at 700° C. for 7 hours. The structure of thematerial obtained, as verified by X-rays, corresponds to that publishedfor triphyllite. The amount of carbon present in the sample has beendetermined by elemental analysis, and gave a concentration of 0.56%. Forcomparison purposes, a similar sample has been prepared in similarconditions, but without the addition of polypropylene powder. Thislatter sample also shows a pure crystalline structure of the typeLiFePO₄.

[0056] Electrochemical Properties

[0057] The materials prepared were tested in button batteries of theCR2032 type at room temperature and 80° C.

[0058] Tests at 80° C. (polymer electrolyte)

[0059] The materials obtained above have been tested in button batteriesof the CR2032 type. The cathode were obtained by mixing together theactive material powder with carbon black (Ketjenblack®) to ensure theelectronic exchange with the current collector, and polyethylene oxidewith a molecular weight of 400000 is added as both a binder and an ionicconductor. The proportions, by weight, are 35:9:56. Acetonitrile isadded to the mixture to dissolve the ethylene polyoxide. The mixture ishomogenized and poured on a stainless steel disc of 1.7 cm². The cathodeis dried under vacuum, and transferred in a Vacuum Atmospheres glovebox, under helium atmosphere (<1 vpm H₂O, O₂). A sheet of lithium (27μm) laminated on a nickel substrate is used as the anode. The polymerelectrolyte comprises polyethylene oxide of weight 5000000 and LiTFSI(lithium bis-trifluoromethanesulfonimide) in proportions of oxygen ofoxyethylene units/lithium of 20:1.

[0060] The electrochemical experiments were carried out at 80° C.,temperature at which the ionic conductivity of the electrolyte issufficient (2×10⁻³ Scm⁻¹). The electrochemical studies are performed byslow voltammetry (20 mV.h⁻¹) controlled by a battery cycler of theMacpile® type. The batteries were charged and discharged between 3.7 and3 V.

[0061]FIG. 2 illustrates the first cycle obtained for carbonaceous andnon-carbonaceous materials prepared above. For the non-carbonaceoussample, the oxidation and reduction phenomenons extend trail over a widepotential range. For the carbonaceous sample, the peaks are much betterdefined on a narrow potential domain. The evolution of both materialsduring the first 5 cycles is very different FIG. 3). For thecarbon-coated sample, die oxidation and reduction kinetics become fasterand faster, thus leading to better defined peaks (larger peak currentsand narrower peak widths). However, for the non-carbonaceous sample, thekinetics become slower and slower. The evolution of the capacity of bothsamples is illustrated in FIG. 4. For the carbonaceous sample, thecapacity exchanged is stable. It represents from 94 to 100% of thetheoretical capacity (170 mAh.g⁻¹) depending on the sample. The initialcapacity of the non-carbonaceous material is around 145 mAh.g⁻¹, i.e.,about 85% of the theoretical capacity. For this sample, the capacityexchanged quickly decreases. After 5 cycles, the battery has lost 20% ofits initial capacity.

[0062] The carbonaceous sample is cycled under an intentiostatic modebetween 38 and 3 V with fast charging and discharging rates. The imposedcurrents correspond to a C/l rate, which means that all the capacity isexchanged in 1 hour. These cycling results are shown in FIG. 5. Thefirst 5 cycles arc performed under a voltamperometric mode to activatethe cathode and determine its capacity. In this instance, 100% of thetheoretical capacity is exchanged during the first voltammetric cyclesand 96% during the first 80 intentiostatic cycles. Subsequently, thecapacity slowly decreases, and after 1000 cycles, 70% of the capacity(120 mAh.g⁻¹) is still exchanged at this rate. The cycling in thepotentiodynamic mode performed after 950 cycles show that in reality,89% of thc initial capacity is still available at slower dischargesrates. The loss of power is associated with the increase of theresistance at the lithium/polymer electrolyte interface. The parameter(capacity passed during charging)/(capacity passed during discharging)become erratic in appearance. This parameter C/D, shown on FIG. 5 at theend of cycling, leads to the presumption that dendrites are formed.

[0063] Tests at Room Temperature (Liquid Electrolyte)

[0064] The LiFePO₄ coated with a carbonaceous deposit was also tested atroom temperature. In this instance, the composite cathode is prepared bymixing the active material with carbon black and EPDM (preferablydissolved in cyclohexane) in ratio 85:5:10. The mixture is spread onto astainless steel current collector in the form of a disc of 1.7 cm²,dried under vacuum, and kept in a glove box under helium atmosphere. Asabove, lithium is used as the anode. Both electrodes are separated by aCelgard™ porous membrane. The electrolyte used in a LiTFSI 0.8 molalsolution in gamma-butyrolactone. The voltamperograms illustrated in FIG.6 were obtained at room temperature under is slow voltammetry (20mV.h⁻¹) between 3 and 3.8 V. With such configuration, the oxidation andreduction kinetics appears to be much slower than at 80° C. Further, thepower of the battery decreases slowly during cycling. On the other hand,the entire theoretical capacity is accessible (97.5% cycle 1, 99.4%cycle 5), i.e., reversibly exchanged without loss during cycling (5cycles). It is not excluded that the low power of 2 0 this battery maycome from a poor permeation of the electrode by the electrolyte, thelatter being a poor wetting agent for the binding polymer.

[0065] The example illustrates that the improvement of the materialstudied, because of the presence of the carbonaceous deposit at thesurface of thc particles, is reflected on the kinetics, the capacity andthe cyclability. Further, its role is independent from that of the typeof carbon black added during the preparation of composite cathodes.

EXAMPLE 2

[0066] This example shows the formation of a conductive carbonaceousdeposit from a hydrocarbon gas. The synthesis described in Example 1 forthe preparation of lithium iron phosphate is repeated without addingpolypropylene powder, and by replacing the thermal treatment inertatmosphere with a mixture of 1% propene in nitrogen. During the thermaltreatment, propene decomposes to form a carbon deposit on the materialbeing synthesized. The resulting sample obtained contains 2.5% ofcarbon, as determined by chemical analysis. Cyclic voltammetry isperformed on this sample under the conditions described in Example 1 decarbon, and shows the important activation phenomenon during the firstcycles (see FIG. 6). The improvement in redox kinetics is accompanied inthis instance by an increase of the capacity reversibly exchanged. Asmeasured during the discharge step, the initial capacity of the LiFePO,sample prepared represents 77% of the theoretical capacity, taking intoaccount the 2.5% electrochemically inactive carbon. After 5 cycles, thecapacity reaches 91.4%. The activation phenomenon observed is linked tothe thickness of the carbon layer eventually porous coating theparticles and capable of slowing the diffusion of the cations.

[0067] The following examples 3-5 illustrate the treatment of thecomplex oxide, namely the lithium iron phosphate LiFePO₄, preparedthermally and independently in order to obtain a conductive carbonaceouscoating.

EXAMPLE 3

[0068] The tryphilite sample LiFePO₄ prepared above is analyzed. Itsmass composition is: Fe: 34.6, Li: 4.2%, P: 19.2, which represents a 5%difference with respect to the stoichiometry.

[0069] The powder to be treated is impregnated with an aqueous solutionof commercial sucrose, and dried. The amount of solution is selected tocorrespond to 10% of the weight of sucrose with respect to the weight ofthe material to be treated. Water is completely evaporated underagitation to obtain a homogeneous distribution. The use of sugarrepresents a preferred embodiment because it melts before beingcarbonized, thereby provided a good coating of the particles. Itsrelatively low carbon yield after pyrolysis is compensated by its lowcost.

[0070] The thermal treatments are performed at 700° C. under argonatmosphere. The temperature is maintained for 3 hours. Elementalanalysis shows that this product contains 1.3% by weight of carbon Suchthermal treatment leads to a black powder giving an electronicconductivity measurable with a simple commercial ohm-meter. Itselectroactivity, as measured on the 1^(rst) (FIG. 8) and 5^(th) (FIG. 9)charge-discharge cycle, is 155.9 mAhg⁻¹ and 149.8 mAhg⁻¹ respectively,which is 91.7% and 88.1% of the theoretical value. These values are tobe compared with that of the product not coated with the carbon deposit,that has only 64% electroactivity. After 5 cycles, this value fades to37.9% (FIG. 10).

EXAMPLE 4

[0071] Cellulose acetate is added to the phosphate LiFePO₄ of Example 3as a precursor of the carbon coating. This polymer is known to decomposewith high carbonization yields, on the order of 24%. It decomposesbetween 200 and 400° C. Above this temperature, the amorphous carbonrearranges to give a graphite-type structure that favors coherent andhighly conductive carbon deposits.

[0072] Cellulose acetate is dissolved in acetone in a ratiocorresponding to 5% by weight of the material to be treated, and driedbefore proceeding as above. The carbon concentration of the finalproduct is 1.5%. The thermal treatment leads, in a similar manner, to ablack powder having surface electronic conductivity, Itselectroactivity, as measured on the 1^(rst) (FIG. 8) and 5^(th) (FIG. 9)charge-discharge cycles, is 152.6 mAhg⁻¹ and 150.2 mAhg⁻¹ respectively,which is 89.8% and 88.3% of the theoretical value. This value is to becompared with that of the product not coated with the carbon deposit,that has only 64% electroactivity. After 5 cycles, this value fades to37.9% (FIG. 10).

EXAMPLE 5

[0073] Perylene and its derivatives are known to lead, after pyrolysis,to graphitic-type carbons, because of the existence of condensed cyclesin the starting molecule. In particular, the perylene-tetracarboxylicacid anhydride decomposes above 560° C. and provides very coating carboncoatings. However, this product shows a poor solubility, and theirintimate mixture with the complex oxide, here also LiFePO₄.of Example 3,is difficult to embody. To solve this problem, a polymer containingperylene groups separated with an ethylene polyoxide chain has beenprepared in a first step. The oxyethylene segments are selected to besufficiently long to act as solubilizing agents for the aromatic groupsin the usual organic solvents. Therefore, commercial3,4,9,10-perylenetetracarboxylic acid anhydride (Aldrich) is reactedwith Jeffamine 600 (Hunstmann) at high temperature, according to thefollowing reaction:

[0074] whereinR=—[CH(CH₃)CH₂O—]_(p)(CH₂CH₂O—)_(q)[CH₂—CH(CH)₃O]_(p−1)CH₂—CH(CH)₃—1≦p≦2;10≦n≦14

[0075] The synthesis is completed within 48 hours in dimethylacetamideunder reflux (166° C.). The polymer formed is precipitated in water, anda solid-liquid separation is carried out. It is purified by dissolutionin acetone, followed by re-precipitation in ether. The process allowsthe removal of unreacted starting materials, as well as low massproducts. The powder is finally dried.

[0076] Carbonization yield of this product is of the order of 20%. Thepolymer is dissolved in dichloromethane in a ratio corresponding to 5%of the weight of the material to be treated before proceeding asdescribed above in Examples 3 and 4. The carbon content of the finalproduct is 1%. The thermal treatment leads, as described above, to ablack conductive powder. Its electroactivity, as measured on the 1^(rst)(FIG. 8) and 5^(th) (FIG. 9) charge-discharge cycles, is 148.6 mAhg⁻¹and 146.9 mAhg⁻¹ respectively, which is 87.4% and 86.4% of thetheoretical value. This value is to be compared with that of the productnot coated with the carbon deposit, that has only 64% electroactivity.After 5 cycles, this value fades to 37.9% (FIG. 10).

EXAMPLE 6

[0077] This example illustrates the use of an elimination reaction froma polymer to form a carbonaceous deposit according of the invention.

[0078] Ferric iron sulfate Fe₂(SO₄)₃ with a “Nasicon” orthorhombicstructure was obtained from commercial hydrated iron (III) sulfate(Aldrich) by dehydration at 450° C. under vacuum. With cooling, andunder stirring, the powder suspended in hexane was lithiated withstoichiometric 2M butyl lithium to reach the compositionLi_(1.5)Fe₂(SO₄)₃. 20 g of the resulting off-white powder were slurriedin 100 ml acetone and 2.2 gram of poly(vinylidene bromide)(—CH₂CBr₂)_(n)— were added and the mixture was treated for 12 hours in aball mill with alumina balls. The suspension thus obtained was dried ina. rotary evaporator and crushed as coarse powder in a mortar. The solidwas treated with 3 g of diazabicyclo [5.4.0]unde-7-cene (DBU) inacetonitrile under reflux for three hours. The black powder thusobtained was filtered to eliminate the resulting amine bromide and isexcess reagent, rinsed with acetonitrile and dried under vacuum at 60°C. Further annealing of the carbonaceous deposit was performed underoxygen-free argon (<1 ppm) at 400° for three hours.

[0079] The material coated with the carbonaceous material was tested for20 electrochemical activity in a lithium cell with a lithium metalelectrode, 1 molar lithium bis-(trifluoromethanesulfonimide) in 50:50ethylene carbonate-dimethoxyethane mixture as electrolyte immobilized ina 25 82 m microporous polypropylene separator. The cathode was obtainedfrom the prepared redox material mixed with Ketjenblack™ and slurried ina solution of ethylene-propylene-diene polymer (Aldrich), the ratio ofsolids content being 85:10:5. The cathode mix was spread on an expandedaluminium metal grid and pressed at 1 ton cm⁻² to a resulting thicknessof 230 μm. The button cell assembly was charged (the tested materialbeing the anode) at 1 mAcm⁻² between the cut-off potentials of 2.8 and3.9 volts. The material capacity is 120 mAhg⁻¹, corresponding to 89% oftheoretical value. The average potential was obtained at 3.6 V vs.Li⁺:Li°.

EXAMPLE 7

[0080] This example illustrates the use of a nitrogen-containingcompound as electrode material.

[0081] Powdered manganous oxide MnO and lithium nitride, both commercial(Aldrich) were mixed in a dry box under helium in a 1:1 molar ratio. Thereactants were put in a glassy carbon crucible and treated under oxygenfree nitrogen (<1 vpm) at 800° C. 12 g of the resulting oxynitride withan antifluorite structure Li₃MnNO were added to 0.7 g of micrometer sizepolyethylene powder and ball-milled under helium in a polyethylene jarwith dry heptane as dispersing agent and 20 mg of Brij™ 35 (ICI) assurfactant. The filtered mix was then treated under a flow ofoxygen-free nitrogen in a furnace at 750° C. to ensure decomposition ofthe polyethylene into carbon.

[0082] The carbon-coated electrode material appears as a black powderrapidly hydrolyzed in moist air. All subsequent handling was carried outin a dry box wherein a cell similar to that of Example 6 was constructedand tested for electrochemical activity of tie prepared material. Theelectrolyte in this case is a mixture of commercial tetraethylsulfamide(Fluka) and dioxolane in a 40:60 volume ratio. Both solvents werepurified by distillation over sodium hydride (under 10 torrs reducedpressure for the sulfamide). To the solvent mixture, is added lithiumbis-(trifluoromethanesulfonimde) (LiTFSI) to form a 0.85 molar solution.Similarly to the set-up of Example 6, the cell comprises a lithium metalelectrode, the electrolyte immobilized in a 25 μm porous polypropyleneseparator and the material processed in a way similar to that of Example6.

[0083] The cathode is obtained from the prepared redox material mixedwith Ketjenblack™ and slurried in a solution of ethylene-propylene-dienepolymer, the ratio of solids content being 90:5:5. The cathode mix ispressed on an expanded copper metal grid at 1 ton cm⁻² with a resultingthickness of 125 μm. The button cell assembly is charged at 0.5 mAcm⁻²(the oxynitride being the anode) between the cut-off potentials of 0-9and 1.8 volts. The materials capacity was 370 mAhg⁻¹, i.e., 70% of thetheoretical value for two electrons per formula unit. The averagepotential is found at 1.1 V vs. Li⁺:Li°. The material is suited for useas negative electrode material in lithium-ion type batteries. Anexperimental cell of this type has been constructed with the electrodematerial on a copper metal grid similar to that tested previously and apositive electrode material obtained by chemical delithiation of thelithium iron phosphate of Example 1 by bromine in acetonitrile. The iron(no) phosphate obtained was pressed onto an aluminium grid to form thepositive electrode and the 0.85 M LiTFSI tetraethylsulfamide/dioxolanesolution used as electrolyte. The average voltage of such cell is 2.1volts and its energy density, based on the weight of the activematerials, is 240 Wh/Kg

EXAMPLE 8

[0084] Lithium vanadium (III) phosphosilicateLi_(3.5)V₂(PO₄)_(2.5)(SiO₄)_(0.5), having a “Nasicon” structure wasprepared in the following manner:

[0085] Lithium carbonate (13.85 g), lithium silicate Li₂SiO₃ (6.74 g),dihydrogen ammonium phosphate (43.2 g) and ammonium vanadate (35.1 g)were mixed with 250 mL of ethylmethylketone and treated in a ball millwith alumina balls in a thick-walled polyethylene jar for 3 days. Theresulting slurry was filtered, dried and treated in a tubular furnaceunder a 10% hydrogen in nitrogen gas flow at 600° C. for 12 hours. Aftercooling, 10 g of the resulting powder were introduced in a planetaryball mill with tungsten carbide balls. The resulting powder was added toa solution of the polyaromatic polymer prepared in Example 5(polyoxyethylene-co-perylenetetracarboxylicdimide 0.8 g in 5 mLacetone), well homogenized, and the solvent was evaporated.

[0086] The red-brown powder was thermolyzed in a stream of oxygen-freeargon at 700° C. for 2 hours, leaving after cooling a black powder witha measurable surface conductivity. The material coated with thecarbonaceous material was tested for electrochemical activity in alithium-ion cell with a natural graphite electrode (NG7) coated on acopper current collector and corresponding to 24 mg/cm², 1 molar lithiumhexafluorophosphate in 50:50 ethylene carbonate dimethylcarbonatemixture as electrolyte immobilized in a 25 μm microporous polypropyleneseparator. The cathode was obtained from the lithium vanadiumphosphosilicate mixed with Ketjenblackk™ and slurried in a solution ofvinylidenefluoride-hexafluoropropene copolymer in acetone, the ratio ofsolids content being 85:10:5. The cathode mix was spread on an expandedaluminium metal grid and pressed at 1 ton cm⁻² to a resulting thicknessof 190 μm corresponding to a active material loading of 35 mg/cm². Thebutton cell assembly was charged (the tested material being the anode)at 1 mAcm⁻² between the cut-off potentials of 0 and 4.1 volts. Thecapacity of the carbon coated material was 184 mAhg¹, corresponding to78% of the theoretical value (3.5 lithium per unit formula), with a slowfading with cycling. In a comparative test, a similar cell constructedusing instead the uncoated material, as obtained after milling the heattreated inorganic precursor but omitting the addition of the perylenepolymer, shows a capacity of 105 mAhg⁻¹, rapidly fading with cycling.

EXAMPLE 9

[0087] This example illustrates the formation of a carbonaceous coatingsimultaneous to a variation of the alkali metal content of the redoxmaterial.

[0088] 13.54 g of commercial iron (III) fluoride (Aldrich), 1.8 g of thelithium salt of hexa-2,4-dyine dicarboxylic acid are ball milled in athick-walled polyethylene jar with alumina balls, in the presence of 100mL of acetonitrile. After 12 hours, the resulting slurry was filteredand the dried powder is treated under a stream of dry, oxygen-freenitrogen in a tubular furnace at 700° C. for three hours. The resultingblack powder contained from elemental analysis Fe: 47%, F: 46%, Li:1.18%, C: 3.5%, corresponding to the formula Li_(0.2)FeF₃C_(0.35). Theelectrode material was tested for its capacity in a cell similar to thatof Example 6 with the difference that the cell is first tested ondischarge (the electrode material as cathode), and then recharged. Thecut-off voltages were chosen between 2.8 and 3.7.Volts. The experimentalcapacity on the first cycle was 190 mAhg⁻¹, corresponding to 83% of thetheoretical value. For comparison, a cell with FeF₃ as the electrodematerial and no carbonaceous coating has a theoretical capacity of 246mAhg⁻¹. In practice, the first discharge cycle obtained in similarconditions to the material of the invention is 137 mAhg⁻¹.

EXAMPLE 10

[0089] This example illustrates also the formation of a carbonaceouscoating simultaneous to a variation of the alkali metal content of theredox material.

[0090] Commercial polyacrylic acid of molecular weight 15000 wasdissolved as 10% solution in water/methanol mixture and titrated withlithium hydroxide to a pH of 7. 4 μL of this solution were dried in thecrucible of a thermogravimetry air a 80° C. to evaporate thewater/methanol. The heating was then continued to 500° C., showing aresidue of 0.1895 mg of calcination residue as lithium carbonate.

[0091] 18.68 g of commercial iron (III) phosphate dihydrate, (Aldrich),8.15 g lithium oxalate (Aldrich), 39 mL of the lithium polyacrylatesolution, 80 mL of acetone and 40 mL of 2,2-dimethoxy acetone as waterscavenger were ball milled in a thick-walled polyethylene jar withalumina balls. After 24 hours, the resulting slurry was filtered anddried. The resulting powder was treated under a stream of dry,oxygen-force nitrogen in a tubular furnace at 700° C. for three hours,resulting in a blackish powder. The resulting product had the followingelemental analysis: Fe: 34%, P: 18.8%, Li: 4.4%, C: 3.2%. The X-rayanalysis- confirmed the existence of pure triphilite LiFePO₄ as the solecrystalline component. The electrode material was tested for itscapacity in a cell similar to that of Example 1 with a PEO electrolyte,and then recharged. The cut-off voltages were chosen between 2.8 and 3.7V. The experimental capacity on the first cycle was 135 mAhg⁻¹,corresponding to 77% of the theoretical value, increasing to 156 mAhg⁻¹(89%) while the peak definition improved with further cycling. 80% ofthis capacity is accessible in the potential range 3.3-3.6 V vs.Li⁺:Li°.

EXAMPLE 11

[0092] The compound LiC_(0.75)Mn_(0.25)PO₄ was prepared from intimatelyground cobalt oxalate dihydrate, manganese oxalate dihydrate anddihydrogen ammonium phosphate by firing in air at 850° C. for 10 hours.The resulting mauve powder was ball milled in a planetary mill withtungsten carbide balls to an average grain size of 4 μm. 10 g of thiscomplex phosphate were triturated in a mortar with a 10 mL of 6%solution of the perylene polymer of Example 5 in methyl formate. Thesolvent rapidly evaporated. The resulting powder was treated under astream of dry, oxygen-free argon in a tubular furnace at 740° C. forthree hours, resulting in a black powder. The electrochemical activityof the cell was tested in a lithium-ion cell similar to that of Example6. The electrolyte was in this case lithium bis-fluoromethanesulfonimide(Li[FSO₂]₂N) dissolved at a concentration of 1M in theoxidation-resistant solvent dimethylamino-trifluoroethyl sulfamateCF₃CH₂OSO₂N(CH₃)₂. When initially charged, the cell showed a capacity of145 mAhg⁻¹ in the voltage window 4.2-4.95 V vs. Li⁺:Li°. The batterycould be cycled for 50 deep charge-discharge cycles with less than 10%decline in capacity, showing the resistance of the electrolyte to highpotentials.

EXAMPLE 12

[0093] The compound Li₂MnSiO₄ was prepared by calcining the gelresulting from the action of a stoichiometric mixture of lithium acetatedihydrate, manganese acetate tetrahydrate and tetraethoxysilane in a80:20 ethanol water mixture. The gel was dried in an oven at 80C for 48hours, powdered and calcined under air at 800° C. 3.28 g of theresulting silicate and 12.62 g of lithium iron phosphate from Example 3were ball milled in a planetary mill similar to that of Example 11, andthe powder was treated at 800° C. under a stream of dry, oxygen-freeargon in a tubular furnace at 740° C. for 6 hours. The complex oxideobtained after cooling has the formulaLi_(1.2)Fe_(0.2)P_(0.8)Si_(0.2)O₄. The powder was moistened with 3 mL ofa 2% solution of cobalt acetate, then dried. The powder was treated inthe same tubular furnace at 500° C. under a flow of 1 mL/s of 10% carbonmonoxide in nitrogen for two hours. After cooling, the resulting blackpowder was tested for electrochemical activity in conditions similar tothose of Example 1. With a PEO electrolyte at 80° C., the capacity wasmeasured from the cyclic voltamogram curve at 185 mAhg⁻¹ (88% of theory)between the cut-off voltages of 2.8 and 3.9 V vs. Li⁺:Li°. The uncoatedmaterial tested in similar condition has a specific capacity of 105mAhg⁻¹.

EXAMPLE 13

[0094] Under argon, 3 g of lithium iron phosphate from Example 3 wassuspended in 50 mL acetonitrile to which was added 0.5 g ofhexachlorocyclopentadiene and 10 mg oftetrakis(triphenylphosphine)nickel (0). Under vigorous stirring, wasadded dropwise 1.4 mL of tetrakis(dimethylamino)ethylene at roomtemperature. The solution turned blue, and after more reducing agent hasbeen added, black. The reaction was left under stirring for 24 hoursafter completion of the addition. The resulting black precipitate wasfiltered, washed with ethanol and dried under vacuum. Annealing of thecarbon deposit was performed at 400° C. under a flow of oxygen free gasfor 3 hours. The resulting black powder was tested for electrochemicalactivity in conditions similar to those of Example 1. The measuredcapacity between the cut-off voltages of 2.9 and 3.7 V vs. Li⁺:Li° wasfound experimentally at 160 mAhg⁻¹ (91% of theory). The uncoatedmaterial has a specific capacity of 112 mAhg⁻¹ in the same experimentalconditions.

EXAMPLE 14

[0095] The spinel compounds Li_(3.5)Mg_(0.5)Ti₄O₁₂ was prepared bysol-gel technique using titanium tetra(isopropoxide) (28.42 g), lithiumacetate dihydrate (35.7 g) and magnesium acetate tetratydrate (10.7 g)in 300 mL 80:20 isopropanol-water. The resulting white gel was dried ina oven at 80° C. and calcined at 800° C. in air for 3 hours, then under10% hydrogen in argon at 850° C. for 5 hours. 10 g of the resulting bluepowder were mixed with 12 mL of a 13 wt % solution of the celluloseacetate in acetone. The paste was dried and the polymer carbonized inthe conditions of Example 4 under inert atmosphere at 700° C.

[0096] The positive electrode of an electrochemical super-capacitor wasbuilt in the following manner. 5 g of carbon coated LiFePO₄ from Example3, 5 g of Norit®, activated carbon, 4 g of graphite powder (2 μmdiameter), 3 g of chopped (20 μm long aluminium fibers (5 mm diameter),9 g of anthracene powder (10 μm) as a pore former and 6 g ofpolyacrylonitrile were mixed in dimethylformamide wherein the polymerdissolved. The slurry was homogenized and coated onto an aluminium foil(25 μm) and the solvent was evaporated. The coating was then slowlybrought to 380° C. under nitrogen atmosphere. The anthracene evaporatesto leave a homogeneous porosity in the material and the acrylonitrileundergoes thermal cyclization to a conductive polymer consisting offused pyridine rings. The thickness of the resulting layer is 75 μm.

[0097] A similar coating is done for the negative electrode with aslurry where LiFePO₄ is replaced with the coated spinel as preparedabove. The supercapacitor assembly is obtained by placing face to facethe two electrodes prepared separated by a 10 μm-thick polypropyleneseparator soaked in 1 molar LiTFSI in acetonitrile/dimethoxyethanemixture (50:50). Tic device can be charged at 30 mAcm⁻² and 2.5 V anddelivers a specific power of 3 kW/L⁻¹ at 1.8 V.

EXAMPLE 15

[0098] A light modulating device (electrochromic window) was constructedin the following manner.

[0099] LiFePO₄ from Example 3 was ball mulled in a high energy mill toparticles of an average size of 120 nm. 2 g of the powder were mixedwith a 1 mL of a 2 wt % solution of the perylene-co-polyoxyethylenepolymer of Example 5 in methyl formate. The paste was triturated toensure uniform distribution of the polymer at the surface of theparticles, and the solvent was evaporated. The dry powder was treatedunder a stream of dry, oxygen-free nitrogen in a tubular furnace at 700°C. for three hours to yield a light gray powder.

[0100] 1 g of the carbon coated powder was slurried in a solution of 1.2g polyethyleneoxide-co-(2-methylene)propane-1,3-diyl prepared accordingto J. Electrochem. Soc., 1994, 141(7), 1915 with ethylene oxide segmentsof molecular weight 1000, 280 mg of LiTFSI and 15 mg of diphenylbenzyldimethyl acetal as photoinitiator in 10 mL of acetonitrile. The solutionwas coated using the doctor blade process onto an indium-tin oxide (ITO)covered glass (20 S⁻¹□) to a thickness of 8 μm. After evaporation of thesolvent, the polymer was cured with a 254 nm LTV light (200 mWcm⁻²) for3 minutes.

[0101] Tungsten trioxide was deposited by thermal evaporation ntoanother ITO covered glass to a thickness of 340 mL The device assemblywas done by applying a layer of a polyethylene oxide (120 μm)electrolyte with LiTFSI in an oxygen (polymer) to salt ratio of 12,previously coated on a polypropylene foil and applied to the WO₃-coatedelectrode using the adhesive transfer technology. The two glasselectrodes were pressed together to form the electrochemical chain:

[0102] glass/ITO/ WO₃/PEO-LiTFSI/LiFePO₄ composite electrode/ITO/glass

[0103] The device turned blue in 30 seconds upon application of avoltage (1.5 volts, LiFePO, side being the anode) and bleached onreversal of the voltage. The light. transmission is modulated from 85%(bleached state) to 20% (colored state).

[0104] While the invention has been described in connection withspecific embodiments thereof, it will be understood that it is capableof further modifications, and this application is intended to cover anyvariations, uses or adaptations of the invention following, in general,the principles of the invention, and including such departures from thepresent description as come within known or customary practice withinthe art to which the invention pertains, and as may be applied to theessential features hereinbefore set forth, and as follows in the scopeof the appended claims.

What is claimed is:
 1. An electrode material comprising a complex oxidecorresponding to the general formula A_(a)M_(m)Z_(z)O_(o)N_(n)F_(f)wherein: A comprises an alkaline metal; M comprises at least onetransition metal, and optionally at least one a non-transition metal, ormixtures thereof, Z comprises at least one non-metal; O is oxygen; Nnitrogen and F is fluorine; and the coefficients a, m, z, o, n, f≧0 andare selected to ensure electroneutrality, wherein a conductivecarbonaceous material is deposited homogeneously on a surface of thematerial to obtain a substantially regular electric field distributionon the surface of material particles.
 2. Material according to claim 1wherein the carbonaceous material deposit is obtained by pyrolysis oforganic matter.
 3. Material according to claim 1 wherein the transitionmetal comprises iron, manganese, vanadium, titanium, molybdenum,niobium, tungsten, zinc and mixtures thereof, the non-transition metalcomprises magnesium and aluminum, ate non-metal comprises sulfur,selenium, phosphorous, arsenic, silicon, germanium, boron, and mixturesthereof.
 4. Material according to claim 3 wherein the transition metalcomprises iron, manganese, vanadium, titanium, molybdenum, niobium andtungsten in the following oxidation states: Fe²⁺, Mn²⁺, V²⁺, V³⁺, Ti²⁺,Ti³⁺, Mo³⁺, Mo⁴⁺, Nb³⁺, Nb⁴⁺ and W⁴⁺.
 5. Material according to claim 1wherein the carbonaceous material precursor comprises hydrocarbons andtheir derivatives, perylene and its derivatives; polyhydric compoundsand their derivatives; a polymer or a mixture of polymers, and mixturesthereof.
 6. Material according to claim 5 wherein the precursor comprisea polymer.
 7. Material according to claim 6 wherein the polymercomprises polyolefins, polybutadienes, polyvinylic alcohol, phenolcondensation products, polymers derived from furfurylic alcohol,polymers derivatives of styrene, divinylbenzene, acrylonitrile, vinylacetate, cellulose, starch and its esters, and mixtures thereof. 8.Process for the deposition of a conductive carbonaceous material asdefined in claim 7 on an electrode material, wherein the polymer orpolymer mixture is dispersed with the complex oxide, followed by apyrolysis under vacuum or under a non-reactive gas atmosphere. 9.Process for the deposition of a conductive carbonaceous material asdefined in claim 7 wherein a monomer or monomer mixture is added to thecomplex oxide, followed by polymerization thereof, and a pyrolysis undervacuum or under a non-reactive gas atmosphere.
 10. Process for thedeposition of a conductive carbonaceous material as defined in claim 1wherein the source of carbon is carbon monoxide alone or in admixturewith an inert gas, and that the deposit is obtained bydisproportionation equilibrium 2CO

C+CO₂ at a temperature lower than 900° C., optionally in the presence ofa catalyst.
 11. Process for the preparation of an electrode materialaccording to claims 1 wherein deposition of the carbonaceous material isperformed at least partially by pyrolysis of an organic derivative of analkaline metal A bringing the fraction a-a′ of the alkaline metal fromthe complex oxide A_(a)′M_(m)Z_(z)O_(o)N_(n)F_(f) in order to leaveafter pyrolysis a carbonaceous deposit at the surface of the complexoxide having a composition of A_(a)M_(m)Z_(z)O_(o)N_(n)F_(f), such thata-a′>0.
 12. Material according to claim 1 wherein the final massconcentration of carbonaceous material is comprised between 0.1 and 55%.13. Material according to claim 1 comprising the complex oxide comprisesis sulfates, phosphates, silicates, oxysulfates, oxyphosphates,oxysilicates, and mixtures thereof, of a transition metal and lithium,and mixtures thereof.
 14. Material according to claim 1 wherein thecomplex oxide is of the general formula Li_(1+x)MP_(1−x)Si_(x)O₄ orLi_(1+x−y)MP_(1−x)Si_(x)O_(4−y)F_(y) wherein is greater of equal to 0≦x,y≦1 and M comprises Fe or Mn.
 15. Material according to claim 1 whereinthe complex oxide is of general formulaLi_(3−x+z)M₂(P_(1−x−z)S_(x)Si_(z)O₄)₃ wherein M comprises Fe or Mn, 0≦xand z≦1.
 16. Material according to claim 1 wherein the complex oxide isof general formulaLi_(3+u−x+z)V_(2−z−w)Fe_(u)Ti_(w)(P_(1−x−z)S_(x)Si_(z)O₄) orLi_(4+x)Ti_(4+x−2y)Mg_(y)Ti₅O₁₂, wherein x is ≦0; w≦2; y≦1 and z≦1. 17.An electrochemical cell wherein at least one electrode comprises atleast one electrode material according to claim
 1. 18. A cell accordingto claim 17 operating as a primary or secondary battery, supercapacitor,or light modulating system.
 19. A cell according to claim 18 that is aprimary or a secondary battery, wherein thc electrolyte is a polymer,solvating or not, optionally plasticized or gelled by a polar liquidcomprising in solution one or more metallic salts.
 20. A cell accordingto claim 18 that is a primary or a secondary battery wherein theelectrolyte is a polar liquid immobilized in a microporous separator.21. A cell according to claim 19 wherein one of the metallic salts is alithium salt.